This invention relates to instrumentation packages, and in particular, to an apparatus for pivotally mounting an instrument package to a line, such as a balloon tether line, to enable the instrument package to freely rotate about the line.
It is a problem in the field of balloon mounted instrument packages to provide an apparatus that enables a user to quickly, simply and reliably attach an instrument package to a balloon tether line in a manner that enables the instrument package to freely rotate about the line. To minimize the size of the balloon required, tether lines are typically constructed from a material with a high strength to weight ratio. However, these tether lines are susceptible to breakage from abrasion, twisting, and kinking stresses. Thus, instrument package attachment systems for tethered balloons must be lightweight, simple to operate, and yet prevent the instrument package from slipping, which causes abrasion of the tether line. The instrument package must also be free to rotate about the tether line with the wind direction to prevent the instrument package from twisting the tether line. Finally, the instrument package attachment system must be constructed with a low profile to reduce wind resistance, which could cause the instrument package to kink the tether line.
There have been a number of past solutions to this problem. The most effective is that disclosed in U.S. Pat. No. 5,410,918, entitled xe2x80x9cAmbient Air Sampler.xe2x80x9d The line attachment apparatus disclosed in U.S. Pat. No. 5,410,918 comprises a stationary axle which is secured to the tether line at respective ends of the axle. End caps fit over the ends of the axle and are received by bearings that are secured to a mounting plate on the air sampler. The bearings allow the air sampler to rotate about the end caps of the axle while the tether line is held stationary within the axle. The mounting plate includes an upper mounting arm fixedly connected to an upper cylindrical bearing and a lower spring-loaded mounting arm connected about a pivot to a lower cylindrical bearing. The spring biases the lower spring-mounted arm into a locked position to hold the axle between the two bearings. The tether line is wound about the axle and secured parallel to the length of the axle by the end caps. A helical groove formed on the outer surface of the axle guides and seats the tether line around the axle when the ends of the axle are inserted into the end caps. A slot or notch formed at each end of the axle receives the line as it exits the groove. The end caps are secured over the two ends of the axle respectively via set screws that frictionally secure the end caps to the axle. Each of the end caps are cylindrically shaped and include a slot formed in the circumference thereof to enable the axle and its attached tether line to be inserted therein and spring loaded into place.
Unfortunately, wrapping large diameter tether lines around the axle is difficult and time consuming. Additionally, the tension generated by a large balloon often prevents the user from gaining sufficient slack in the tether line to enable wrapping about the axle. Furthermore, the use of the end caps to both secure the tether line to the axle and provide the bearing function places a significant amount of stress on the end caps. This results in premature wear or the need to utilize expensive materials in the construction of the end caps.
The above described problems are solved and a technical advance achieved in the art by the present instrument package mounting apparatus for pivotally mounting an instrument package to a line. The instrument package mounting apparatus comprises an axle, a pinch bar and a pair of bearings. The axle comprises an elongated cylindrical body having an interior channel configured to receive the tether line and the pinch bar. The pinch bar is tapered and configured to insert into the channel with the tether line to frictionally secure the axle to the tether line using a compression connection created by the taper of the pinch bar as the pinch bar is inserted. A slot juxtaposed to the interior channel and extending substantially the length of the axle provides access to the interior channel for receiving the tether line. At least one end of the axle includes an aperture for insertion of the pinch bar into the channel to frictionally secure the axle to the tether line. The bearings terminate the ends of the axle to provide a rotational attachment to an instrument package. In particular a first one of the bearings is connected to a first end of the axle and a second one of the bearings is connected to a second end of the axle to provide the rotational attachment to the instrument package. The bearings permit the instrument package to freely rotate about the axle, which internally secures the tether line via that friction force generated by the tapered pinch bar.
In some examples of the present instrument mounting apparatus, the axle comprises a two piece axle design, wherein a first and a second segment of the axle each comprise mating segments of a cylindrical solid that define the interior channel and the slot juxtaposed to the channel. A plurality of fasteners secure the first and second axle pieces together. In addition, the respective bearing connected to each end of the axle provides further reinforcement of the connection between the first and second axle pieces.
In other examples of the present instrument package mounting apparatus, the axle comprises a three piece axle design. In particular a first segment, a second segment, and a third segment each comprise mating segments of the cylindrical solid that define the interior channel and the slot juxtaposed to the channel. The first segment, the second segment, and the third segment are assembled by fasteners, which are tightened to secure the second segment and third segment to the first segment. As with the prior example, the respective bearing connected to each end of the axle provides further reinforcement of the connection between the first, second, and third axle pieces.
A first advantage of the present instrument package mounting apparatus is that the slot and channel can be configured in a plurality of dimensions to accommodate various tether line sizes. A second advantage of the present instrument package mounting apparatus is that it receives the tether line internal to the axle. This eliminates the prior art requirements of generating enough slack in the tether line to wrap the tether line about the axle and align the tether line with the helical grooves at each end of the axle. A third advantage of the present instrument package mounting apparatus is that the axle and the pinch bar provide the attachment to the tether line thereby eliminating the need for the end caps of the prior art. A fourth advantage of the present instrument package mounting apparatus is that the tether line is frictionally secured to the axle in a substantially uniform manner along the length of the axle to eliminate stress points. A fifth advantage of the present instrument package mounting apparatus is that grooves in the channel could be used to accommodate various sizes of tether line without reconfiguration of the axle.